The use of a time-slot differentiated electricity rate system for leveling the power demanded of a power supplier can lower an electricity rate of a general household. For example, when the time-slot differentiated electricity rate system is used, the electricity rate is approximately 9 yen/kWh between 11 p.m. and 7 a.m., approximately 23 yen/kWh between 5 p.m. and 11 p.m. and between 7 a.m. and 10 a.m., and approximately 28 to 33 yen/kWh between 10 a.m. and 5 p.m.
The lowest electricity rate between 11 p.m. and 7 a.m. is approximately ⅓ of the electricity rate obtained between 10 a.m. and 5 p.m. In the present specification, information pertaining to these power usage time slots and the electricity rates is referred to as “time-slot differentiated electricity rate information”.
Hereinafter, the time-slot differentiated electricity rate information indicating the time slot between 11 p.m. and 7 a.m. is described as a lowest electricity rate time slot.
Examples of an electric device that is operated in a programmed manner in accordance with the lowest electricity rate time slot (between 11 p.m. and 7 a.m.) include a storage type electric water heater such as a heat pump water heater or an electric boiler. The electric water heater boils water and stores the boiled water during the lowest electricity rate time slot, and allows the hot water to be consumed during daytime when the electricity rate is the highest. The all-electric houses equipped with this kind of storage type water heater have been increasing in recent years.
Furthermore, in addition to the electric water heater, examples of an electric device requiring a large amount of electricity include heating and cooling equipment such as an air conditioner, cooking equipment such as a rice cooker, and household equipment such as a clothes washer, a clothes dryer and a dish washer/dryer. A user of such an electric device operates the equipment while being conscience of the lowest electricity rate time slot or sets timers of the equipment so that the equipment operate during the lowest electricity rate time slot.
Not only these electric devices but also energy storage devices have been increasing. For example, a rechargeable battery of an electric vehicle, a plug-in vehicle or a two-wheeled electric vehicle can be charged at home. If there is a rechargeable battery at home, excess power can be charged into the rechargeable battery, and the rechargeable battery is discharged when power is needed. The recent technical innovation and the rise of the oil prices indicate that electric vehicles and two-wheeled electric vehicles are becoming more popular. In most cases, on-board batteries of electric vehicles and two-wheeled electric vehicles need to be charged at home, which implies a definite increase in the number of users who drive or wish to drive these vehicles in accordance with the lowest electricity rate time slot.
On the other hand, an upper limit of a household power usage is specified in a contract. Use of power exceeding the contract power (allowable power) throws an ampere breaker serving the whole house. Therefore, when the household equipment described above are operated intensively during the period between 11 p.m. and 7 a.m. producing the lowest electricity rate, the ampere breaker is likely to be thrown in the middle of the night. If the user does not notice that the ampere breaker is off, in the morning the user not only sees the water not boiling or the rice not cooked in the programmed rice cooker, but also cannot use his/her electric vehicle because the rechargeable battery thereof is not charged.
In other words, when intensively operating the household equipment at night after setting the timers thereof, the user needs to make sure that the amount of electricity consumed does not exceed the allowable power.
The above has described examples of the use of electricity in a general household. However, not only general households but also business offices, factories and commercial facilities such as stores that use various electric devices and electric transporting vehicles have contract powers, which are the upper limits of electricity usages, and are demanding to use the electric device efficiently at low electricity rates within the range of the contract powers.
There exists a conventional invention (see Patent Literature 1 and Patent Literature 2, for example) that performs control to reduce the amount of power consumed in a charger in consideration of the amount of power consumed in a house, so that the amount of power consumed does not exceed a contract power or allowable power when operating an electric device and charging a rechargeable battery of an electric vehicle at the same time at night.
Patent Literature 1 describes an on-board battery charger that reduces the amount of charging current used for charging a home battery or an on-board battery, when the current exceeds a contract current as a result of using a microwave. This on-board battery charger controls the current immediately before the contract power is exceeded, but does not systematically control the current based on the current used by the microwave and the current used for charging the batteries.
Patent Literature 2 describes a charging power management system that creates a residential estimated power load map to adjust the amount of power consumed between the beginning of charging of an on-board battery and the end of the charging, so as not to exceed a contract power.
Patent Literature 3 describes a charge control device and method that are not for performing the control to prevent a breaker from being thrown when electric devices are operated at the same time as when a rechargeable battery of an electric vehicle is charged, but for creating, in a car rental office where a plurality of electric vehicles are charged, for example, a charging plan based on a start time for using each vehicle and a necessary charge amount required for each vehicle to reach its destination. This technology uses a car navigation device for computing the start time and the necessary charge amount required for each vehicle to reach its destination.
However, according to the conventional methods, the microwave or other electric devices that a user wishes to use immediately is operated at the same time as when an electric device such as a charger of an on-board battery is operated, which can be used by the user any time. For this reason, during a period in which the microwave is preferentially used, the amount of power consumed for charging the on-board battery can be controlled to be lower than the contract power. Because the abovementioned cooking equipment is normally used in a relatively short period of time (approximately several minutes to a little over ten minutes at the longest), the amount of power consumed during this period can be given up temporarily without causing any major adverse effects where, for example, water is not boiled when needed or the electric car does not move due to its weak battery. However, when using, at home, an electric water heater that needs continuous supply of power for a relatively long period of time and an electric car that needs to be charged for a relatively long period of time, a time period during which the power is supplied to the electric water heater should not overlap with a time period during which an on-board battery of the electric car is charged, so that these equipment do not compete over the electricity.
It is obvious that the best way is to end the boiling performed by the electric water heater and the charging of the on-board battery within the lowest electricity rate time slot, but this might cause a tremendous trouble when either one of the equipment needs to be used preferentially to reduce the amount of power consumed in the other. In other words, what is expected is that the water in the electric water heater is not boiled when needed, and therefore hot water is not available, or that the battery of the electric car is not charged enough to be able to drive it to the destination.
Moreover, the distance that the electric car travels varies so significantly from day to day that the remaining level of the on-board battery fluctuates at a charging start time point.
Needless to say, there are no problems if the remaining level of the on-board battery is high. However, when the electric car travels a significantly long distance and the remaining level of the on-board battery is extremely low, uncertain situations occur where a long charging time is required or larger current charging needs to be performed, making a power control operation extremely difficult. Particularly, even when the on-board battery is charged after the electric water heater finishes boiling water, the charging might not be ended fully by the next morning.
In the conventional power control operation that combines the electric car and the microwave or other electric devices used for a short period of time, there is a problem that cannot be solved when combining an electric water heater and an electric car that uses large current for a long period of time.
Because a rechargeable battery of an electric vehicle basically cannot be charged while in use outside, except when the rechargeable battery is charged quickly using a charging station, it is preferred that the rechargeable battery be charged as much as possible while the electric vehicle is at home or at work. Although the conventional methods are effective in this case, there remains a basic problem where the charging plan cannot be created until the electric vehicle is connected to the charger at home.
In other words, the electric device is operated during the lowest electricity rate time slot, not knowing when the electric vehicle returns home. When the electric vehicle returns home during the operation of the electric device, the charging plan that gives the highest priority to charging of the electric vehicle needs to be created, which in turn requires readjustment of the operation for supplying power to the operating electric device or to electric device planning to be operated.
For example, suppose that the electric vehicle returns home around 11:30 p.m. when a clothes washer/dryer is used after 11 p.m. during the lowest electricity rate time slot (11 p.m. to 7 a.m.).
When the operation of the clothes washer/dryer is stopped until the electric vehicle is charged completely in order to prioritize charging of the electric vehicle, the clothes are immersed in detergent in the washer for several hours, which can damage the clothes. Thus, the electric vehicle needs to be charged after the operation of the clothes washer/dryer is ended.
Another example is an electric water heater that boils water during the lowest electricity rate time slot. The boiled water is stored in a storage tank. The storage tank is made to retain heat. It is preferred that the electric water heater boil water immediately before the obtained hot water is used. Therefore, the water is boiled immediately before 7 a.m. so that the obtained hot water can be used when setting the table for breakfast or washing the dishes after the breakfast. Suppose that the electric water heater is programmed to boil water around, for example, 5 a.m.
At this moment, suppose that the electric vehicle returns home around 5 a.m. In order to use the electric vehicle at 8 a.m., charging of the electric vehicle is preferentially performed immediately after the electric vehicle returns home. Meanwhile, the boiling of the electric water heater is stopped until the charging of the electric vehicle is ended. Then, the electric water heater starts boiling the water as soon as the charging of the electric vehicle is ended.
However, when the charging takes too much time and the boiling does not end past 7 a.m., the hot water cannot be used for setting the table for breakfast. In addition, there is a possibility that a large amount of power is supplied to the electric water heater after the lowest electricity rate time slot.
In the prior arts, therefore, the charging plan that prioritizes charging of the electric vehicle is created after the electric vehicle returns home, and thus cannot be coordinated with the operation of other electric devices, depending on when the electric vehicle returns home.